This invention relates to a magnetic bubble memory device. More particularly, the present invention is concerned with a magnetic bubble memory device having a decreased stress on patterns made of soft magnetic materials and an improved adhesion of a passivation film.
It has been a usual practice in a conventional magnetic bubble memory device to form a passivation film 6 directly on the pattern 5 using SiO.sub.2 which is an inorganic matter after formation of a pattern 5 made of a soft magnetic material as shown in FIG. 1. In this case, the coercive force Hc of the pattern 5 made of a soft magnetic material increases due to the influence of stress of the SiO.sub.2 passivation film 6. Such an influence becomes remarkable with the reduction in magnetic bubble diameter and reduction in minimum feature of patterns made of soft magnetic materials, which causes the propagation margin of the magnetic bubble to be degraded. The same is true in a hybrid magnetic bubble memory device comprising hybrid type tracks composed of ion-implanted propagation tracks and soft magnetic material propagation tracks. Specifically, in a hybrid magnetic bubble memory device, the formation of a passivation film 6 made of SiO.sub.2 after the formation of the pattern 5 made of a soft magnetic material as shown in FIG. 2 bring about an increase in coercive force Hc of the pattern 5 made of a soft magnetic material as in the above-mentioned magnetic bubble memory device, which is a major causative factor of the degradation of the propagation margin. In this connection, it is noted that, since the hybrid magnetic bubble memory device uses ion-implanted propagation tracks in its minor loop, the major part of the device comprises the ion-implanted track. Therefore, the hybrid magnetic bubble memory device has a large area where a second insulator film 4 is in direct contact with the SiO.sub.2 passivation film 6. In order to reduce the step caused in the pattern 5 made of a soft magnetic material which crosses a conductor pattern 3, a heat-resistant polymer has been used as the second insulator film 4. Examples of the heat-resistant polymer include a polyimide resin, an epoxy resin, a phenolic resin, a polycarbonate resin, a polyamide-imide resin, a polybenzimidazole resin and a silicone resin. However, since such heat-resistant polymers are poor in adhesion to SiO.sub.2, there arises a large problem of reliability.
In order to eliminate the above problem related to the adhesion, Japanese Patent Laid-Open No. 28517/1980 has proposed to use a resin as the passivation film. Although the use of the resin as the passivation film improves the adhesion to the second insulator film, the passivation film comprising the resin is poor in protective ability against mechanical shock and environmental humidity, which makes a device unsuitable for a practical use.
As is apparent from the foregoing, the above-mentioned conventional magnetic bubble memory devices had problems with respect to the stress or adhesion of the passivation film and, therefore, had disadvantages such as degradation of the propagation margin and poor reliability.